Color photography



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YELLOW Mnaewm suemncrws DYES c YA N YELLOW mean/m c Y/w SUBTRACT/VE DY${COEREtT/I'E FINAL POSITIVE Patented Jan. 9, 1940 UNITED STATES PATENTOFFICE COLOR PHOTOGRAPHY Application March 21,

7 Claims.

This invention relates to color photography and more particularly tocolor photography of the subtractive type involving the use of asubtractive film which records the diflerent color aspects of the scenethroughout the same area, although in certain aspects the invention maybe utilized with other types of film. Examples of film of the type towhich this invention is particularly applicable are known asscreen-plate film, monopack film, etc. In the latter type, for example,the film may comprise a transparent base carrying on one side thereof aplurality of coatings differently sensitized to record different coloraspects of a scene. Usually three such coatings are provided, first ared-sensitized layer, secondly a superposed green-sensitized layer, andthirdly an ordinary blue-sensitive layer. Intermediate non-sensitizedcoatings may be provided to serve as filters or separators or both. By asingle exposure in an ordinary camera latent negatives of three-coloraspects are formed in the three layers respectively, leaving sufflcientunexposed silver halide in each layer to form a corresponding positiveby reversal. The layers are then subjected to suitable development toconvert the exposed silver halide into silver, after which the silver isdissolved or bleached out. By reexposing the film, said unexposed silverhalide is exposed to form latent positives, and then, by suitabledeveloping treatments, the latent positives are converted into coloredpositives, for example as described in the Troland Reissue Patent No.18,680, Capstafi No. 1,954,346 and in various other so-called monopackpatents to Mannes and G three coloring-matters constituting thephotograph should absorb only one-third of the spectrum withoutappreciable absorption of the remaining two-thirds. For example, anideal cyan (minus red) would absorb red light but neither green norblue, anideal magenta (minus green) would absorb green light but neitherred nor blue, and an ideal yellow (minus blue) would absorb blue lightbut neither red nor green. However, the available coloring-matters donot in general meet these ideal requirements. While there are yellowdyes-which absorb little if any light other than blue, the bestavailable magenta color absorbs considerable blue light as well as greenand the best available cyan absorbs both green and blue light as well asred. Indeed I have found that one of the best non-fugitive cyancoloringmatters for absorbing red light has approxi- 1986, Serial No.70,048

mately 50% as much absorption of green light and approximately 25% asmuch absorption of blue light; and one of the best non-fugitivemagentas. for absorbing green light has approximately 50% as muchabsorption of blue light.

Thus the best available cyan coloring-matter may be regarded as amixture of ideal cyan and 50% as'much ideal magenta and 25% as muchideal yellow, and the best available magenta as including 50% as muchideal yellow. I

These imperfections alter the proportions in which the three colors mustbe used in order to obtain neutral balance, that is colorless whites,grays and blacks. For example if the cyan acts as though it contained50% ideal magenta, the theoretical amount of magenta has to be reduced50%; and if each of the cyan and magenta pigments contributes of thenecessary yellow eflect the theoretical amount of yellow must also bereduced 50%. While this adjust- 2o ment produces neutral balance in thewhites, grays, and blacks of the picture, the colored portions,especially the green portions, are dull.

This effect is'not ruinously great in a direct color picture of a scene,but if one attempts to 25 reproduce such a photograph directly byprinting on similar film, the combined effect of the two sets ofimperfections causes a two-fold color degradation which has heretoforerendered impractical such reproduction of color photographs.

The principal object of the present invention is to correct for theinaccuracies of available coloring-matters and to counteract theaforesaid dulling effect on the colored portions of the picture, whencolor prints are to be made from an original color photograph. Otherobjects will appear from the following description and the appendedclaims.

' Inasmuch as the method herein disclosed and claimed is in the natureof an improvement on that disclosed and claimed in my copendingapplication Serial No. 35,323 filed August 8, 1935, reference is made tothat application as a background for the present disclosure. Furtherobjects of the present invention are to' reduce the 4 number of stepsdescribed in the aforesaid application and to increase the sharpness ofdefinition in the corrected color photograph.

As in my prior method the present invention involves the formation ofintermediary and cor- 5o rective films for use in making the correctedcolor print, but this improved method involves an essential departurefrom the former procedure. Instead of printing the corrected picturefrom intermediary records made from other intermediaries in two or moresuccessive printings, I print it directly from the original colorpicture in connection with a superposed corrective record whichfurnishes the desired color correction without interfering substantiallywith the drawing of the picture. Said drawing, being applied directlyfrom the original to the print in a single printing, carries the fullsharpness of the original, avoiding cumulative loss of definition due tosuccessive printings.

Said, corrective may either be made'of a single film capable, likemonopack film, of recording more than one color component, or a separatefilm for each color component. In the latter case the films preferablycarry the photographic images or records'in-the form of dyed reliefs. Imake the corrective film or films from the original film and twointermediary negatives made on I panchromatic stock, the first printedfrom the gamma of unity, and the second printed from the first and theoriginal in combination with a green filter. These films, in combinationwith the original, are then printed with color filters on the correctivefilm or films in two printings,

and the latter are processed appropriately to develop the color images.The final print is then made in one printing from the original andcorrective film or films. It will be understood that, in this context,the term negative means of opposite sign so that the intermediarynegative of an original film negative (as for example an unreversed filmof the Kodachrone type) would actually be a positive of the objectfield.

sometimes desirable to' obtain double or triple correction. In fact,since this process is particularly adapted for making corrected colorprints from original color photographs, there are usual- Q ly at leasttwo sets of coloring-matters involved for which a double correction willthus be needed to reproduce the original scene rather than the originalcolor photograph. The degree of. correction needed depends, not only onthe number of pigment sets involved, but also on the degree ofimperfection of their spectral absorption and on the photographic systemused; e. g., a subtractive original will ordinarily require more anddifierent corrections from an additive or screenplate original.

I obtain various degrees of correction by varying the nature of thefilms on which the correctives are made, or the processing to which theyare subjected, the degree of correction being in general proportional tothe contrast or gamma of the corrective emulsions as processed. Forinstance, when dyed-reliefs are used as correctives, the degrees ofcorrection is proportional to the density of dye put into the reliefs,and may be varied accordingly by washing and redyeing them. For doublecorrection, i. e., to make the color print reproduce the original scenewhen using pigments having absorptions as hereinbefore given, the gammaof the corrective film should be three, in both the magenta and yellowcomponents. For a single correction, with the same colors, it should beunity. In both these cases, for the same pigments, the gamma of thesecond negative should be approximately two.

Each printing operation should be suificient to bring the entire printedimage within the straight-line portion of the characteristic curve; andthe aforesaid first negative should be deyeloped to a gamma ofapproximately one as noted. The various prints may be made byconoriginal with a red filter and developed to a.

As explained in my prior application it is .aieaosc tact or projectionprinting; but since each operation except the first involves printing apicfore corrective prints, projection printing affords better definitionin the printed picture except in g the case of the first printing.

For the purpose of illustration typical applications of the inventionare shown diagrammatically in the accompanying drawing in which:

Fig. 1 illustrates the complete procedure using a single corrective filmon multicolor film stock such as monopack; and

Fm. 2 illustrates the complete procedure, using two corrective films inthe form of dyed-reliefs.

In each of the figures the three-color transparency such as a monopackfor example, is indicated by yellow shading Y, magenta shading M andcyan shading C. The original color'picture to. be reproduced isdesignated P, the intermediary negatives as N and N, the unitarycorrective print as K, the two dyed-relief corrective prints K and K",and the corrected reproduction as P'.

Referring to Fig. 1, the first operation is to print the panchromaticfilm N from the original picture- P, through a red filter RF, asindicated by the arrow l, and develop it in the ordinary way to a gammaof unity. This print is registered with the original P in a projectionprinter, and as indicated by arrow 2 the sandwich" is printed 'through agreen filter on panchromatic film N which is then developed. Thus therecord in film N is a negative of the cyan record of P (the red aspectof the scene); and the record in film N is across between a negative ofthe magenta record of P (the green aspect of the scene) and a positiveof the cyan record of P (the red aspect of the scene).

N and N are then registered with the original picture P and printed witha blue filter .BF on color-recording film such as monopack, which is toform the corrective film K, as indicated by the arrow 3. The negative Nis registered with P and printed with a green filter GF, as indicated bythe arrow 4, on the same corrective film K, which is then processed todevelop the color records, as positives, preferably by reversal, theblue-filter printing appearing as a yellow record Y" and thegreen-filter printing as a magenta record M. x

The gammas or relative contrasts of these color records must in generalvbe greater than those of the commercial monopack film known asKodachrome. For obtaining correct reproduction of the original scene onthe final print, in the case where the'pigments of both the initial andthe final color pictures are approximately those hereinbefore specified,said gammas should be approximately three. For merely duplicating theoriginal color picture without further color armors 4 yellow records inK and give correct color balance) on ordinary monopackfilm (suitable fortaking original pictures), as indicated by the arrow 5, to print thecorrected reproduction P 5 which is processed in appropriate knownmanner.

To avoid having to obtain or prepare and process the specialhigh-contrast monopack film suitable for making the unitary correctiveK, I may use instead two monochrome corrective films or simpler typewhich may preferably be dyed-relief films, made by reversal or the likeprocess to produce positive color records. The process is shown in Fig.2. The one receiving the blue printing is dyed yellow. and the onehaving. the 5 green printing is dyed magenta. The gammas are asspecified for the monopack corrective, and may be governed by the depthof dyeing applied to the reliefs. The two must .both be registered withthe original in a projection-printer ior makzo ing the final correctedprint. Apart from this, the process is identical with that alreadyoutlined,

as will be apparent from Fig. 2.

The fact that the corrective film or films carry little of thedrawingoi' the picture will be evident from a brief consideration of thespecial case of a neutral or colorless scene where the corrective filmhas no contrasts or density difierences at all.

In a neutral color picture-the densities to red,

green and blue light are all equal. When N is printed and developed to agamma of unity, it becomes a negative of the redabsorbin'g image in P,so that when it is registered with P, all variations of the cyan orred-absorbing image are neutralized, resulting in a uriii'ormdensity forred light and, the color densities being equal and the silver of thenegative being neutral in color, this is true for green and blue" lightaswell; and since N is printed through the uniform densities of I thecombination of P and N, it also hasa-uniiorm density. Then the printingsthrough P and'N (arrow 4) and through l?,'N and N (arrow 3) all carryuniform light exposures to the film K and produce uniform densities,with no outlines or drawing" whatever.

the most brilliant colors. Thereforei'thecorrec-e ll tive has littleefiect on the sharpness of outline in any ordinary picture.

From the foregoing it will be evident that the (flesh-pink being nearlya neutral color in this sense) it will be evident that definition in thecorrected reproduction depends mainly on the to original film alone. g

It should be understood that the present disclosure is for the purposeof illustration only and I that this invention includes allmodifications and equivalents which fall within the scope'oi the 70appended claims.

I claim: 1. The method of reproducing a color picture by superimposingrecords of several color aspects,

involving deficient coloring matter properly ab- 75 sorbing lighttransmitted by the taking filter of and printing color correctedreproductions from Thus it is evident 7 that j to density differences onK (also on N') do. not; represent difierences'oi light and shade in thepicture, which vary widely,- but onlycolor. dii'l'erences, which aremuch lessextremeior all butv 3 its color aspect but improperly absorbinglight which should only be abmrbed by coloring matter for a secondaspect, which'method comprises making a photographic record of said.first color aspect oi the picture, said record and said first 5 aspectbeing oi opposite sign, printing from said first record in register withsaid color picture a colored corrective record combined from said recordand said second aspect, and then printing a corrected picture with saidcolor picture and said 9 I corrective record in registered combination.

2. The method. of reproducing a color picture by superimposing recordsof several color aspects, involving deficient coloring matter. properlyabsorbing light transmitted by the taking filter of 15 its color aspectbut improperly absorbing light which should only be absorbed by coloringmatter for a second aspect, which method comprises making'a negativerecord of said first color aspect oi the picture, with light 01 thetaking color a of said first aspect, printing from said negative record,in registered combination with said color picture, a colored'correctiverecord with printing light of the color of said second aspect, and thenprinting'a corrected picture with said color pictureand said correctiverecord in registered combination.

3. The method of reproducing a color origina by superimposing records ofseveral color aspects, involving deficient coloring matter properly ab-30 sorbing light transmitted by the taking filter oi its color aspectbut improperly absorbing light which should only be absorbed by coloringmatter for a second aspect, which method comprises making an uncolorednegative record of said first color aspect of the original, printingfrom said negative record in registered combination with saidoriginal acolored corrective record combined from said negative record and saidsecond aspect,

said original and said colored record in registered combination.

4. The method of reproducing a color picture by superimposing records oiseveral color aspects, involving deficient coloring matter properlyabsorbing light transmitted by the taking filter of its color aspect butimproperly absorbing light which should only be absorbed by coloringmatters for a second aspect and a third aspect, respectively, whichmethod comprises making a negative record of said first color aspect ofthe picture, rnaking an uncolored. corrective record of the picture byprinting said second color aspect in register with said negative record,printing from said negative and said corrective records 55 bysuperimposing records 01. several color aspects,

involving deficient coloring matter properly absorbing light transmittedby the taking filter of its color aspect but improperly absorbing light.which should only be absorbed by coloring matters forasecond aspect anda third aspect, re-

. spectively, which method comprises making a negative record of saidfirstcolor aspect of the picture by developing it to a gamma oi unity,making an uncolored corrective record 01 the picture by printing saidsecond color aspect in register with said negative record and developingit to a gamma higher than unity, printing from said 76 negative and saidcorrective records in register with said-color picture a coloredcorrective record combined from said negative and uncolored records andsaid third aspect, and then printing a corrected picture with said colorpicture and said corrective record in registered combination.

6. The method of reproducing a color picture by superimposing records ofthe r d, green and blue color aspects, involving deficient coloring,

grand said corrective record in registered coina on.

t I. The method of reproducing a color picture by superimposing recordsoi thered, green and blue color aspects; involving deiicient coloringmatter properly absorbing red light but improperiy absorbing greenlight, which method comprises printing a negative record from thepicture with red light, printing irom said record in registeredcombination with said picture, a corrective green absorbing record withgreen light, and then printing with blue-green light a corrected picturefrom said colo'r picture and said corrective record in registeredcombination.

EASTMAN AQWEAVIR.

